Tuned radio frequency amplifying system



May 7, 1929.

L. .L. JONES TUNED RADIO FREQUENCY AMPLIFYING SYSTEM Filed May 27, 1924 2 Sheets-Sheet 1 INVENTOR Lesier L. Jones lls ORNEY6 May 7, 1929. v L. L. JONES TUNED RADIO FREQUENCY AMPLIFYING SYSTEM.

Filed May 27, 1924 2 Sheets-Sheet 2 (um O Audib Sfagg Z Ra d 5o Sfage l Rad 1o Stage INVENTOR Lesrgr L. Jones 7 A TTORNEYS Patented May 7, 1929.

UNITED STATES LESTER L. JONES, OF ORADELL, NEW JERSEY.

.TUNED RADIO FREQUENCY AMPLIFYING SYSTEM.

Application filed May 27, 192-1.

This invention relates to tuned cascaded circuits embodying one or more electron discharge devices or tubes, and relates more particularly to an improved tuned radio frequency amplifying systen'i.

The invention has special reference to the provision of a tuned radio frequency amplil'ying system designed and constructed for producing a maximum amplification citiciency con'ibined with a nraxinunn selectivity over a large wave length range, and for permitting etlicient controlling, neutralizing or compensating of the capacitive feed rack reaction which due to the capacitive coupling between the grid and plate of the tube.

This application is a continuation in part of the following of my copending applications: Capacitive coupling control system. Ser. No. (307.046, tiled Dec. 15. 1922; and Variomcter. Ser. No. ($14,401:, tiled Jan. 23, 1923* now Patent No. 1,664,513 patented April a, 1921s.

A prime desideratum of my present invention centers more specifically about the production of an amplifying system employing tunable circuits coupled in cascade in which the tuning of one of the circuits is accompanied by a predetermined change in the eou 'iling coetlicient between said circuit and an adjacent circuit in order to obtain the maximum amplification efficiency together with a. constant and the greatest. possible selectivity tor each wave length.

A further prime object of my present invention comprehends the provision of an an'mlitying system of the nature referred to embodying one or more electron discharge tubes in which the capacitive coupling coefficient between the input and output circuits of the tube-and the voltage on the plate are maintained constant over the whole wave length range, producing a system in which the energytretranster from the output to the input circuits-due to the grid-plate capacity of the tube is held in ariant. Further and correlated objects "of the invention include the provision of tuned radio frequency amplitying'circuits in'which thetuning is accomplished without producing any material variation in the shunt'capacity of the grid or input circuits of the system, and the provision of a. system of this nature in which the first input circuit is rendered independent of the size of the antenna and is virtually decoupled therefrom.

Serial No. 716,124.

. A still further and correlated prime ob jtCt of my present invention centers about the production ot,tuned cascaded circuits ornbodying one or more electron discharge devices in which any undesirable retransfer 'of energy from the output to the input circuit of the tube due to the grid-plate capacity is etlectively controlled or compensated for in a uniform manner over the whole wave length range of the system.

To the accomplishment of the foregoing and such other objects as will hereinafter appear, my invention consists in the elements and their relation one to the other as hereinafter particularly describedmnd sought to be defined in the claims; reference being had to the accompanying drawing which shows the preferred embodiment of my invention,

and in which:

Fig. 1 is a wiring diagrammatic view showing some of the principles of my invention applied to a radio receiving system of the tuned radio frequency amplifying type, andshowing the use of my variometer and variotranst'ormers for linking the circuits,

the construction and arrangement of the interlinking variometerand variotransformers,

.Fig. 3 is a view showing the manner in which the parts of the variometer are preferably connected,

Figs. 4 and 5 are views respectively of the design of variotransformers employed in the first and second radio frequency stages of the system, and

Fig. 6 is a wiring diagrammatic View of the radio receiving system having two stages of radio frequency amplification and one stage of audio frequency amplification showing the principles otmy invention applied for producing inductive tuning of the interlinked circuits and for controlling the capacitive feed back of the electron discharge devices.

Referring first to Fig. 1 of the drawings, 100

I show the principles of my invention applied to a--radio receiving system of the tuned radio frequency amplification type embodying preferably though not necessarily two stages-of tuned radio frequency amplification. This 105 system comprises a plurality of electron discharge devices 'a, a and a each including a cathode or filament 20, a grid 21. and an anode or plate 22. i The electron discharge device a is provided with an input or grid cir- 110 Fig. 2 1s a view showing diagrammatically discharge device (I and the linking structure cuitgenerally designated as 1' connected to an cncrgv receiving circuit such as the antenna circuit n, and is provided with an output or plate circuit generally designated as 0 which is linked to an input or grid circuit.- i associated with the electron discharge device (1 by means of a Yttllt tItlIlHfUl'lllOl V described more in detail hercina Her and embodying my invention as disclosed and claimed in the aforementioned copcnding application Ser. No. 614.404.

The elec ron discharge device a is also provided with an output or plate circuit 0' which is'linked to an input circuit i associated'with the electron discharge device a by means of a second variotranstormer V The electron V forms the first radio frequency amplification stage, and the electron discharge device. a and the linking structure V forms the second radio frequency amplification stage, the electron discharge tube or device, a? forming the detecting stage, this tube being provided with the output circuit or telephone circuit 0 In the preferred embodiment of my invention, each of the input circuits is inductively tuned, and preferably to the frequency of the radio Waves desired to be selected. For inductively tuning the first input circuit i which connects the grid 21 to the negative terminal of the battery A, the input circuit provided with the variable inductance or variometer V of my invention, the said variometer comprising a stator S and a rotor R each composed preferably of a plurality of coils of the double D type as hereinafter described more in detail, the construction diagrammatically depicted in Fig. 1 showing the double 1) se ctions of the rotor R and the stator S arranged coaxially and connected across the input; cir cult, the opposite ends of the variometer being connected to the antenna n and to ground g.

For inductively tuning the input circuit 5', the variotransforn'ier V comprises a variable secondary L having a construction similar to that of the variometer V and including the coaxially arranged rotor R and stator S each of the double 1) section type, the said variable secondary being connected to the grid 21 of the tube a by means of the conductor 23 and to the negative terminal of the battery A by means of the coni'luctors 2 1, 25 and 26. The primary of the variotransformer V com prises a coil L, which is inductively related to the variable secondary L and preferably coupled to the stator coil S thereof and arranged coaxially with both the stator and rotor of the secondary, all as will be described more in detail hereinafter and as is diagram matically depicted in Fig. l. The primary L is arranged in the output circuit 0 of the first tube a and is connected to the plate 22 by means of the conductor 27 and to the positive terminal of the liiattery B, by means of the conductor 28, the A and 1% batteries being connected together by the conductor 29 as shown in the drawings.

For inductively tuning theinput circuit I the variotrans'tormer V is provided with the variable inductance or secondary L, which includes the rotor 1t and the stator S of the double 1) section type having a construction similar to that heretofore descrilictl in conncc tion with the variotrans'tornun- V, the said secondary L being connected to the grid 21 by means of the conductor 30, the integrating device 31 and conductor 32, and being connected to the positive terminal of the A. battery by the conductors 33, 3-1, 35 and 36. The primary L of the variotransfin-mer V is also arranged coayially with the rotor and stator ot' the secondary as diagrammatically depicted in Fig. l, and is also composed preferably of a coil of the double D section type connected to the plate 22 of the tube a by means of the conductor 37 and to the positive ter' minal of the B battery by means of the conductor 38.

The outputcircuit 0 is provided with the current ('letecting means such as the telephone 39 connected at one end to the plate .22 by m ans ot' the conductor ttl, and at the other end to the positive terminal of the B battery by means of the conductor 41, the usual condenser 42 being connected in shunt to said telephones. For heating the-filaments of all the electron discharge devices to incandescence to produce the electron emission. the same are connected to the A battery, the filament 20 of the device a being connected to one terminal of the battery by means of the conductors 43 and 36, and to the other terminal of the battery by means of the conductor ll, rheostat 45 and conductors 46 and 26, the filament 20 of the device a being similarly connected to the battery A and to the rhcostat 45 by means of the conductors 47 and 48, wh ile the filament 20 of the device a is connected to one terminal of the A battery by means of the conductors 49, 34, 35 and 2-6, and to the other terminal by means of the conductor 50, rheostat 51, and conductors 52, 25, t6 and 26.

As heretofore stated, a prime object of my present invention centers about the produc tion of a system employing tunable circuits coupled in cascade, in which the tuning of one of the circuits is accompanied by a predetermined change in the coupling coetlicient between said circuit and an adjacent circuit. I have discovered by empirical determination in tuned radio frequency amplifying systems, that in order to obtain the maximum amplification etlicieney, together with a constant and the greatest possible selectivity for each wave length, the coupling coetlicient between adjacent circuits should be varied in the same direction and progressively with the wave length variations so that at the smaller waves the coupling should be relatively loose. and at the longer waves relatively close or tight.

To accomplish the desired results, in the preferred embodiment of my invention the coupling between the cascaded circuits is made of the inductive type and the tuning of the circuits is etl'ected inductively as already explained. Although in the preferred emhodiment' I show the inductive coupling combined with the inductive tuning, it will be understood however that the invention is not limited to the inductive coupling and tuning type, and that the principles of the invention may be carried out with other types of coupling and tuning. The inductive type is preferred. however, for the numerous advantages ottered thereby, which will become apparent as the description of the various fez tnres of my invention proceeds.

in this preferred inductive coupling and inductive tuning of the invention, the desired coupling coefficient and tuning variations are produced by the design and construction of the variotransforiners used in the first and second tuning stages. These variotransformer units generally shown in Fig. 1 are diagrainmatically depicted in Figs. 4 and 5 of the drawings. Fig. 4 relating to the variotranstormer used in the first stage. and Fig. 5 to that used in the second stage, the construction of the variable secondary of these 'ariotransformers being more accurately illustrated in Fig. 2 of the drawings, and the connection thereof in Fig. 3 of the drawings.

ltc't'erring first to Fig. 2 of the drawings, the variable secondary or Variometer constructionally comprises a rotor including a set of coils and a stator also including a set oi coils. the coils of the stator set and the coils of the rotor set being arranged in interleaving alternating relation after the main her of thestator and'rotor plates of a variable air condenser, and as shown diagrammatically in Fig. 2 of the drawings, the rotor R comprises the set or plurality of rotor coils 1y, 1",, r and 01, arranged in alternation with the set or plurality of coils 8,, 8,, 3,, and s, of the stator S. The rotor and stator coils, as will he understood, are arranged in closely spaced superposed relation, and are shown in Fig. 2 displaced laterally only for purposes of clarification and for facilitating the tracing of the circuits in the independent stator and rotor coils.

The stator coils are each wound so as to produce a winding in a single plane, the winding comprising two coil sections for producing magnetic fields in opposite directions, each oi the coils to this end comprising the two coil sections and 10 wound in opposite directions and presenting av double D forznation, this being indicated by the arrows showing the momentary direction of flow of current in the windings to produce a field in the coil section 10 in one direction as indicated by the circles ll and a magnetic field in the coil section It) in the oppoiste direction as indicated by the cross 11'. The stator coils are connected together so that their nuituals add, and to this end the oppositely positioned coil sections 10 and 10 are electrically connected by conductors 12 and the end coils are. connected to the terminals 13 and 13 by means of the conductors l2 and 12" respectively. With this arrangement and interconnection, it will be seen that. the magnetic flux threads up through the coil sections on one side and down through the coil sections on the other, producing a magnetic lield which is closed substzmtially within the contiues or dimensions ot" the coils, thus minimizing any external magnetic lield.

The rotor coils '1', to 23, are each. similarly constructed, comprising two sections 1 and 1t producing a double I) coil, the sections being wound in opposite directions as clearly indicated by the arrows in the figure to produce. oppositely directed magnetic fluxes as shown by the circles 15 and the crosses 15. These rotor coils are also interconmzcted so that the mutnals therebetween add, and to this end some of the coil sections let are connected by means of the conductors 1.6 and some of the coil sections 14 are connected by means of the conductors 16, the end coils being connected to the terminals 17 and 17 by means of the conductors 1G and 16" respectively. To obtain the desired direction of the fluxes with this interetmnect'ion, it will be noted that the coils r, and are inversed with respect to the coils r, and 71,, the connection between the coil sections of the first set of coils being on one side of the rotor axis, and the connectitm between the coil sections of the other set being shown on the other side of the said axis. With this arrangement it will be also noted that the magnetic flux threads through all the rotor coil sections in a manner to minimize an external magnetic field.

Still referring to Fig. 2, the rotor coils are shown arranged in alternation with the stator coils, and when the same are superposed in the position shown in Fig. 3, the mutnals oppose to produce aminimum inductance. Vith this construction it. will be seen that as the rotor is rotated from the position shown to a position of 180 thereto, the RltlilltllS will change from full opposing to -tul-l aiding, and in the latter position the tields of equal mag nitude will aid each other to produce a maximum inductance value. To accomplish this latter end, the rotor coils are preferably made equal in number to the stator coils, and are similarly wound to produce like physical dimensions.

lltt

The stator and rotor coils may be connected either in parallel or in series, and when it is desired to connect the stator and rotor coils in series, the manner of connection shown in Fig. 3 of the drawings may he adopted, the stator coils S and the rotor coils It being connectcd together only at one end as shown. With this series connection, a very large inductance and wave, length. range may be ohtaiiied, the distrilulted capacity as represented by the condenser C being somewhat greator than that for the parallel connection.

Referring now to Figs. 4 and 5 of the d rawings, I show the pret'erred design and construction of the variotransformers, each con sisting of the primary L, of the double D type and the secondary 11, which is in all respects like the variometer shown in Fig. 2 and described hereinbelore. The double I) rotor and stator coils are shown in Figs. t and 5 as 1",, 7' 7",, T and 8,, s. 51,, and a, in a coi'iventional manner forqmrposes of simplicity, it being understoml, however, that the design is of the double D type more accurately depicted in Fig. 2. It will be noted that. for the first stage variotransformcr (Fig. 4-) the ])l'lll'ltll' V L, is arranged at the. end of the unit and is coupled to a stator coil (s while for the second stage variotranstormcr (Fig. 5) the primary L, is arranged between the end stator and rotor coils s,-r and is coupled to the stator coil for reasons that will become clearer hereinafter.

To produce the desired coupling and tuning variations, the variotransformer units V and V must be accurately designed, and this incl udes. a (leteri'nination of 1. The maximum and minimum inductance of the secondary L 2. The positioning of the primary or plate coil T1,, and

The magnitude of the mutual M between the rimary L, and the seeondai'y L and the resulting value or magnitude of the. primary, each of which is determined by one or more factors as follows.

(1) F actors dctcrrnhti'no the mam harem and albino/1.20m, oal'ucs 0f the inductance of the secondary.

The maximum wave length desired. and the grid shunt capacity to he used, as hereinafter explained, determine the maximum inductance of the secondary of the variotransformer; and in the preferred construction this is made 640 micro-henrys. The minimum inductance is determined by the shortest wave length required; and this minimum is ohtained by reducing the spacing between the double D coils, the closer the coils the less the magnetic leakage, and the lower the minimum inductance and wave length. In the preferred embodin'ient of the invention, a spacing of two-tenths of an inch between the rotor and stator coils which gives .a minimum inductance of miero-henrys and a ratio of about 8.5 to 1 is used, this being found ample and eflicient for covering the lu'oadcast range of wave lengths.

(13) Factors (Zctcr/nw'nfny //l( position. of {/20 primary 0? p/a/c cm'f.

The position of the primary or plate coil relative to the varionieter or secondary coils depends upon the manner in which it is desired that the coupling coetlieimit or mutual indmrtance vary with the. wave length; and I have empirically demonstrated, as will become clearer presently, that the desired variations should range t'rom(o.) the mutual inductance rarying'somcwliat greater than proportionatcly with the. wave length to the mutual inductance varying as the square of the wave length so that. the. coupling coclticient inerez-ises at. all times with the: wave length of the secondary. In a general way. as will be shown presently. the vru'iation of the mutual inductance is with a higher power of the wave length, the nearer the plate coil is to the center of the Yariometer coils.

For example, in the. Villlt)l'l'tlllSfOllllGl' of my invention I provide two primary-coils 11,, and l -l (see Figs. 4 and 5) only one of which is used as the plate coil. One of these coils is at the outer end of the variotranst'ormer and is separated from the other by the rearmost stator coil 8,. lhe second prin'iary coil is therefore between the rearmoststator and a rotor coil of the variometer. The manner in which the mutual inductance varies With the wave length depends upon which of these two primary coils is used as the plate coil.

In the first stage variotranstormer (Fig. 4) I use, as already stated, the outside coil as the plate. coil, with the result that the mutual inductance varies somewl'iat faster than proportionatcly with the wave length and therefore the Coupling coethcient- K: 11?: v L1L2 increases less than proportionately with the wave length, as will he seen from the following tabulation l A ctual i f Theoret- Vari'oinetcr W W? t :al

In mltl0-g t I henrys 1 Maximum 97 117 N... 0.. 58 l 72 Minimum 25.5 33

Cir

a coupling coefficient varying directly with the wave length; and in this second stage variotransformer, the inside primary coil is used for the plate coil, with the following results:

It will therefore be seen that in the one case I use a coupling coeiiicient which increases slightly with the wavelength, and in the second case 1 use a coupling coefiicient which increases almost exactly proportionatclv with the wave length, and also that the variation is sharper the nearer the plate coil is to the center of the variomoter unit.

(3) Factors determining Hm cud-11c of the mutual inductance and inductance of the plate or primary coil.

l-laving determined the position of the plate coil, from the above considerations (namely the type of variation of mutual inductance or coupling coeflicient desired) I next tix the inductance of the plate coil. This is selected in general so as to get a high amplification cfi'iciency at the long (or any) wave length, and so as to avoid so high an ind nctance as would create a primary circuit nearly resonant. to the shortest wave length. Such a resonant circuit might be formed from the plate and compensator coils shunted by the tube capacity and a portion of the lu'evious input circuit inductance and capacity. For determining the magnitude of the mutual M, recourse must first be had to the factors of amplification efiiciency and selectivity.

(12.) The factor of amplification efiicie'ncy and con/11' f'io ns governing the some.

I have empirically discovered that the highest energy amplification from practically any type of tube is bad by inserting an impedance in the output circuit'of the tube equal to approximately one half the plate filament impedance of the tube. Present day tubes operating with proper C bat- ,terieshave plate filament impedances ranging from 20,000 to 40,000 ohms so that the tube output circuit impedance shouldbe approximately 10,000 to 20,000 ohms and I select an average of 15,000 ohms.

In order to have high amplification eiiiciencv in the tuned amplifier operating over a brohd wave length band. it is highly desirable to hold or maintain this impedanceof the output circuit of the tube up to' approximately 15,000 ohms selected. The impedance of the primary coil is relatively low, having usually an average value Of'abOllt 500 ohms for the broadcast wave length band. The greater part of the output impedance must therefore be the equivalent secondary impedance reflected into the primary. When the secondary is tuned to resonance the resistance reflected in the primary is:

MM h R where M is the mutual, c) is 211' times the oscillation frequency and R, the ohmic resistance of the secondary circuit. R being determined by-considerations of sharpness of tuning, this equation determines M for any given wave length, and therefore the inductance of plate or primary coil. To maintain high amplification eflicicncy this reflected resistance must be held constant over the wave length range, to the output impedancc empirically determined, namely, 15,000 ohms or more (up to 30,000 ohms). \Vith this value of the reflected resistance empirically arrived at, the values of the mutual M and the ohmic resistance R, of the secondary may now be determined.

(6) T he factor of selectivity and conditions gouern'ing the same.

Before completely determining the 'value of M, it is necessary to consider the secondary resistancebecause this is intimately related to the selectivity of the amplifier.

Assuming that it is desired to make each stage as selective as possible, it is necessary to find how far to go. General theory teaches that in order to amplify modulated waves without distortion, the amplifier must transmit all of the wave frequencies carrying the modulated energy. This band of frequencies consists of that group ranging from the carrier frequency less thehighest modulation frequency, to the carrier plus the highest modulation frequency. In a practical way this band is one lying 3,000 cycles each side of the carrier frequency. This condition may be translated into my tuned amplifier design by postulating that the resonant circuit shall be so broadly tuned that the highest and lowestfrequencies of this band shall produce voltage effects no less than of the effect produced by the mean or carrier frequency. To further relate this condition to the resonant circuit of my invention, I may say that. the decrement of the resonant circuit for this broad casting band should be of the order of .02 to satisfy this condition. For example, if a resistance of 2 ohms is given to the secondary circuit at 200 meters, where the inductance is 75 microhenrys and the capacity 150 mfds, the resulting decrement will be .0116. The sharpness of resonance (i. e. the detuning factor for voltage effects) of such a circuit corresponds to 2620 cycles change of frequency at this wave length and to only 850 cycles at 600 meters showing that such low decrement would produce appreciable distortion on the long waves. It will be seen, therefore, that the amplifier should be operated with appreciable ohmic resistance in the secondary circuit.

.llaving found by experiment, that approximately ohms of real ohmic resist.- alu'c in the secondary circuit at 200 meters is required. for stable operation. I insert this value in equation (1), and tind that the necessary mutual is approximately 20 microhcnrys. This value together with the sec-. ondary inductance and the predetermined position of the plate coil as hcreinbctoi" arrived at determines the inductance of the plate coil. In my present embodiment this inductance is about 90 micro-hcnrys.

The foregoing considerations aid in explaining the physical basis of the t'eature of my invention which relates to the sinu'iltaneous increase of coupling co-etticicnt with 'avc length. In the inductively tuned secondary the resistance of the secondary. besides being appreciable as above indicated. should increase with the wave length. The increase of this resistance is determined by two tactors namely, the characteristic ot constant selectivity and the characteristic of t he greatest possible selectivity for each wave length. For obtaining constant selectivity, the log. dec. should be constant, and for obtaining the greatest possible selectivity on all wave lengths, the log. dec. should vary proportionately with the wave length, as given in the following equation:

5 WEN/L2 where R=R +R -R as defined hereinbelow. For constant selectivity since L the inductance of the secondary increases as the square of the wave length, R must increase with the wave length to hold this log. (lee. constant. For obtaining the greatest possible selectivity on all Wave lengths and the log. dec. varying proportionately to the wave length as stated, it follows that R must vary as the square of the Wave length.

The resistance R of the secondary is composed of three parts:

1. The ohmic resistance of the secondary circuit which is designated R 2. The resistance of the primary circuit (substantially the filament plate resistance of the tube) reflected into the secondary circuit which is designated as R 3. The negative resistance introduced into the secondary through the capacitive feed back action of the succeeding plate circuit. This is introduced in the form of a voltage acting on the secondary circuit in phase with the secondary current. This negative re sistance is designated as R I have found that good results are to be obtained when the resistance reflected from the primary into the secondary I is of the same order of magnitude as the ohmic resistance of the secondary. By this I mean that R shall be from 1 to 2 times R. This division leads to freedom from local osciL lations through all practical variations of the tube impedance. The sum of these two is reduced by to because of the subtraction of R Now it we refer to equation (I) :R

we see that. in order to obtain the constant selectivity, the mutual (M) must vary as the power of the wave length, since lb It therefore will be seen that for each stage, to obtain the optimum comlitions, the

3 mutual should vary between the 9 power and the square of; the wave length. lntlle practical embodiment of the invention this range of values is adopted, and as hcrctotorc shown. I select for the second tuning stage ot the system a mutual varying as the square of the wave length, while for the first tuning stage I select a mutual which varies somewhat less than the power of the wave length, the

lesser value being selected for the purpose o't compensating for changes in the losses of the first input circuit which take place with change in wave length, as will be further explained hereinafter.

The above considerations are theoretical and apply more closely to practical cases the greater the number of cascaded stages. assun'iing that all external feed back he eliminated, this for the reason that; all intermediate stages have input circuit resistances which are rcduciliile by an amount corresponding to the tube capacitive feed back reaction, whereas the last stage usually has a higher decrement than the intermediate stages. These theoretical considerations a re important, however, because the selectivity of the system tends to become that power of the selectivity of the average of the selectivitics of each stage corresponding to the number of stages.

The princi 'iles of my invention thus far described show the adaptability of my sys tem to tuned radio frequency circuits in which the capacitive feed back reaction due to the gridplate capacity is compensated for neutralized or suitably controlled.

. the tube may be held In cascaded circuits in which the secondary circuit is capacitively tuned, the

capacitive coupling co-eflicient between the grid and plate circuits of a tube 2 (K= g-, where 0,, is small compared with 0, 0,)

instead of remaining constant,--will vary with the tuning of the secondary, increasing sharply with the decreasing wave length, with the result that the energy retransfer or feed back increases, this energy retransfer being proportional to K x V where V is the voltage on the plate. The ideal con dition is where both K and V are constaut, since it is desired that the feed back due to the capacitive coupling be a constant residual amount (about 3 micro-microfarads) just sufficient to make up for losses in the input circuit of the tube, and not more.

I Capacitive feed back has the effect of decreasing the apparent resistance of the input circuit and thence increasing the current and voltage therein. This should be increased up to a certain point and not beyond, since the more the current is increased, the louder the signal and the more selective the circuits, until a limit is reached, the limit being the stage at which incipient and sus tained oscillations take place. The ideal system, therefore, is one in which the energy retransfer (K x V) is maintained constant over the whole wave length range of the system; and the capacitively tuned system does not meet the requirements because of its variable capacitive coupling coefilcient K! In prior systems in which the capacitive grid-plate feed back is controlled, not only is the value of K variable, but the plate voltage V is variant and in the same direction as K, producing a squared increase of energy feed back with decreasing wave length, instead of holding the energy retransfer constant as desired. This 18 due to the fact. that the inductive couplin coeflicient between the coupled or linke circuits is held constant, causing the output impedance in the plate circuit to decrease with the wave length and consequently the plate voltage increases with the decreasing wave length. 'The combination of these two factors, therefore, produces a negative resistance reaction in the grid circuit which diminishes at least as fast as the square of the wave length, leaving the input circuit with an extremely high decrement on the longer waves.

With the principles of my system, however, I am enabled to design the circuits so as to maintain both the capacitive coupling coefiicient K and the plate voltage V constant over the whole wave length range, producing a system in which the ener retransfer due to the grid-plate capacity of substantially invariant in shunt with over the whole wave length range, and may be controlled for tubes of different gridplatecharacteristics.

The features of my system which permit of this capacitive feed back control are the inductive turning and the inductive coupling coetlicicut variations produced. By means of my inductively tuned circuits, I am enabled in a manner to be described presently tomaintain the capacity of the tunable cir- Cllll) constant during tuning thereof, permitting the capacitive coupling coeflicient K to be held constant, and by means of the above described variation in the inductive coupling coefficient K, the output impedauce (the reflected resistance R,) is constant over the whole wave length range, and this latter produces a plate voltage which remains constant, the plate voltage being the product of the output impedance and the oscillating plate current. The plate voltage herein referred to is not the direct current plate voltage but the alternating voltage on the plate which is the product of the output impedance and the oscillating plat-e current.

To obtain the optimum conditions for holding the capacitive coupling coetlicient K" constant over the whole wave length range, correlated to the inductive tuning of the input circuits I provide means for producing a shunt capacity in each of the input circuits which remains substantially constant during the tuning of the same, this being provided for the antenna input circuit i and for the first and second stage input circuits 2" and i To achieve the desired results the total shunt ca acity of each of the input circuits is made From ten to twenty times and preferably fifteen times the grid-plate capacity of the tube. I have determined that this may be accomplished by placing a condenser the secondary L, of the variotransformers V and V of a value of about 80 micro-micro-farads to bring the total shunt capacity of the input circuits 2" and a" to about 150 micro-micro-farads, and referring to Fig. l of the drawings, these shunt condensers are indicated respectively as m and m respectively.

The provision of these shunt condensers each having the above stated comparative magnitude possesses in general the following advantages:

(a) It makes the wave length calibration of the circuit independent of the tube ca-:

is a coupling that will neutra we the input peso circuit resistance due to the feedback reaction,

(a) It oflers' a ready means of adusting the total circuit capacity to a pr etermined value. This is commercially important in order to have all of the stages of the tube am lifier calibrate the same way. v

lthough I have selected a value of 150 micro-micro-farads for the total shunt capacity, it will be understood that this may e varied within limits. Experimentally have found that the best results are to be secured by using a fixed capacity across the grid circuit of approximately 100 micromicro-farads. The useful ran e forpresentday amplifying tubes and for t c engineering materials avail ble for the construction of the tuned transformers is from 50 to 150 micro micro-farads. This applies more particularly to the present broadcasting range of 200 to 57 5 meters; and for higher wave lengths the shunt grid capacity should be increased approximately proportionately with the wave length. In the present form of my invention I employ, however, a total shunt ca acity of 150 micro-micro-farads as stated. A iigher efliciency may be secured by the use of a total shunt capacity of 100 micro-microfarads, but this optimum value is not desirable because of cost considerations.

The selection of this value of shunt capacity is determined on the one hand by the fact that smaller shunt capacities are open to variation in calibration due to a change of vacuum tube, are subject to change of tuning due to change of filament current, and are subject to excessive capabitive feed, back which is not easil .controllable. The selection is determine on the other hand by the fact that larger shunt capacities make it ex? tremel diiiicult to obtain the high amplification e ciency with the engineering materials commercially available. This is primarily due to the fact that the high output impedances (10,000 to 20,000 ohms) desired to match the output plate-filament impedance are diilicult to build up with high capacity circuits.

The antenna inputcircuit i is similarly provided with a shunt capacity generally designated as m which is placed in shunt wit the variometer V, the shunt capacity having a value of about 60 micro-micro-farads, this capacity functioning to render the tuning of the antenna circuit independent of any capacity changes.

In the preferred embodiment of the invention, the antenna or first input circuit 1' besides being constructed to maintain a constant capacity during, tuning, is designed so as to be rendered independent of the size 2 of the antenna,.the construction including means for effecting a virtual decoupling of the first input circuitfrom the antenna n. This is accomplished by providing a condenser called a series condenser m in series with the antenna n and the variometer V, the size of this condenser being about the capacity of a small antenna, or the capacity of a large antenna. With this construction and with the total shunt capacity of the first input circuit 11, the capacity of the input circuit has a magnitude which is from four to five times the capacit of the antenna and the series condenser com ine With this recited construction I have found that the varioineter V tunes independent of the size. of the antenna and with substantially constant coupling to the antenna over the whole wave length range, the capacity of the first input circuit being therefore localized to the variometer. Besides the man advantages of this tuning system hereinbe ore described, the rendering of the capacity of all of the input circuits lnde endent of the tuning permits the same dia settings for each of the variometer or variotranst'ormer units, so that a mono-control system is afforded.

With the capacities of the input circuits all maintained invariant over the whole wave length range, it will therefore be seen that the antenna capacitive coupling coeflicient is held constant and the capacitive coupling coefficients between the rid and plate circuits of both tuned radio frequency stages are also held constant, producing in combination with the constant plate voltage characteristic, a system in which the product K xV is substantially constant for each stage; and with this product constant, and assuming other factors such as the resistance of the circuits constant, the energy retransfer or feed back due to the grid plate capacity may be held invariant. In the preferred embodiment of the invention, the energy retransfer in the second tuning stage of the system is held constant, while the energ retransfer in the first tuning stage is me e to deviate somewhat from a constant value and more specifically to. decrease with increase of wave length so as to'com of losses in the first input circuit which takes lace with increase 0 wave length, it being ensate for the decrease desired that the ener y retransfer be a conrate less than the power of the wavelength ergy retraiisl'fer in this first tuning stage, however, while it is made to vary for compen sating purposes, changes in the order of the 1 power of the wave length and maybe regarded as substantially constant. p

This result of constant capacitive energy feed back produced with m' system permits the employment of casca ed tubecircuits without means for neutralizing the grid-plate i I I A as heretofore set forth. The change in en v and voltage therein.

creasing the apparent In cascaded circuits in which the secondary circuit is capacitively tuned, the

instead of remaining constant,-will vary with the tuning of the secondary, increasing sharply with the decreasing wave length, with the result that the energy retransfer or feed back increases, this energy retransfer being proportional to K x V where V is the voltage on the plate. The ideal condition is where both K and V are constant, since it is desired that the feed back due to the capacitive coupling be a constant residual amount (about 3 micro-micro farads) just sufficient to make up for losses in the input circuit of the tube, and not more. Capacitive feed back has the etfect of de resistance of the input circuit and thence increasing the current This should be increased up to a certain point and not beyond, since the more the current is increased, the louder the signal and the more selective the circuits, until a limit is reached, the limit being the stage at which incipient and sus' tained oscillations take place. The ideal system, therefore, is one in which the energy retransfer (K' x V) is maintained constant over the whole wave length range of the system; and the capacitively tuned system does not meet the requirements because of its variable capacitive coupling coefiicient In prior systems in which the capacitive grid-plate feed back is controlled, not only is the value of K variable, but the plate voltage V is variant and in the same direction as K, producing a squared increase of energy feed back with decreasing wave length, instead of holding the ener retransfer constant as desired. This is due to the fact that the inductive couplin coeflicient between the coupled or linke circuits is held constant, causing the output impedance in the plate circuit to decrease with the wave length and consequently the plate voltage increases with the decreasing wave length. 'The combination of these two factors, therefore, produces a. negative resistance reaction in the grid circuit which diminishes at least as fast as the square of the wave length, leaving the input circuit with an extremely high decrement on the longer waves.

With the principles of my system, however, I am enabled to design the circuits so as to maintain both the capacitive coupling coefficient K and the plate voltage V constant over the whole wave length range, producing a system in which the energy retransfer due to the grid-plate capacity of the tube may be held substantially invariant capacitive coupling coefficient between the grid and plate circuits of a tube where 0,, is small compared with O, 0,)

over the whole wave length range, and may be controlled for tubes of diti'erent gridplate characteristics.

'lhe features of my system which permit of this capacitive feed back control are the inductive turning and the inductive coupling COQfllClOIlt variations produced. By means of my inductively tuned circuits, I am enabled in a manner to be described presently to maintain the capacity of the tunable circuit constant during tuning thereof, permitting the capacitive coupling coefiicient K to be held constant, and by meansof the above described variation in the inductive cou ling coeflicient K, the output impedance (the reflected resistance R',) is constant over the whole wave length range, and this latter produces a plate voltage which remains constant, the plate voltage being theproduct of the output impedance and the oscillating plate current. The plate voltage herein referred to is not the direct current plate voltage but the alternating voltage on the plate which is the product of the output impedance and the oscillating plate current.

To obtain the optimum conditions for holding the capacitive coupling coefficient K constant over the whole wave length range, correlated to the inductive tuning of the input circuits I provide means for producing a shunt capacity in each of the input circuits which remains substantially constant during the tuning of the same, this being provided for the antenna input circuit 2' and for the first and second stage input circuits 1" and 2' To achieve the desired results the total shunt capacity of each of the input circuits is made from ten to twenty times 'and pref erably fifteen times the grid-plate capacity of the tube. I have determined that this may be accomplished by placing a. condenser in shunt with the secondary L, of the variotransformers V and V of a value of about 80 micro-micro-farads to bring the total shunt capacity of the input circuits 6' and 2' to about 150 micro-micro-farads, and referring to Fig. 1 of the drawings, these shunt condensers are indicated respectively as m and m respectively.

The provision of these shunt condensers each having the above stated comparative magnitude possesses in general the following advantages:

(a) It makes the wave length calibration of the circuit independent of the tube cit-- pacit nitude which 15 a coupling that will neutra I)? It creates a capacitive feed back c0udue to the fact that the circuit resistance due to the feed backreaction,

(c) Itofl'ersaready means of ad'ustin the total circuit capacity to a pr etermined value. This is commercially important in order to have all of the stages of the tube am lifier calibrate the same way. I

lthough I have selected a value of 150 micro-micro-farads for the total shunt caacity, it will be understood that this ma e varied within limits. Experimentally l have found that the best results are to be secured by using a fixed capacity across the grid circuit of approximately 100 micromicro-farads. The useful ran e for present day amplifying tubes and for t e en meering materials available for the construction of the tuned transformers is from 50 to 150 micromicro-farads. This applies more particularly to the present broadcasting range of 200 to 575 meters; and for higher wave lengths the shunt grid capacity should be increased approximately proportionately with t'he wave length. Inthe present form of my invention I employ, however, a total shunt ca acity of 150 micro-microfarads as stated. A liigher efliciency may be secured by the use total shunt capacity of 100 micro-microfarads, but this'optimum value is not desirable because of cost considerations.

The selection of this .value of shunt ca- .acity is determined on the one hand by the act that smaller shunt capacities are open to variation in calibration due to a change of vacuum tube, are subject to change of tuning due to change of filament current, and are subject to excessive capacitive feedv back which is not easil .controllable. The selection is determine on the other hand by the fact that larger shunt capacities make it extremel difficult to obtain the high amplification etli ciency withthe engineering materials commercially available. 'This is primarily high output impedances (10,000 to 20,000 ohms) desired to match the output plate-filament impedance are difficult to build up with high capacity circuits.

The antenna input circuit a is similarly provided withja shunt capacity gen'erall designated as m which is placed in shunt wit the variometer V, the shunt capacity having a value of about micro-micro-farads, this capacity functioning to render the tuning of the antenna circuit independent of any capacity changes.

In the preferred embodiment of the innation, the antenna or first input circuit 1 besides being constructed to maintain a constant capacity during, tuning, is designed so as to be rendered independent of the size of the antenna, the construction including means for effecting a virtual decoupling of the first input circuitfrom the antenna a. This is accomplished by providing a condensor called a series condenser m in series with the antenna 1: and the variometer V, the size of this condenser being about the capacity of a small antenna, OI-'1 o' the capacity of a large antenna.- With this construction and with the total shunt capacity of the first input circuit 2', the capacity of the input circult has a magnitude which is from four to five times the capacit ofthe antenna and the series condenser combined. With this recited construction I have found that the varioineter V tunes independent of the size of the antenna and with substantially constant coupling to the antenna over the whole'wave length range, the capacity of the first input circuit being therefore localized to the variometer. Besides the man advantages of this tuning system hereinbe hre described, the rendering of the capacity of all of the input circuits independent of the tuning permits the same dial settings for each of the variometer or variotransformer units, so that a mono-control system is afforded.

With the capacities of the input circuits all maintained invariant over the whole wave length range, it will therefore be seen that the antenna capacitive coupling coefficient is held constant and the capacitive coupling coeflicients between the rid and plate circuits of both tuned radio Frequency stages are also held constant, producing in combination with the constant plate voltage characteristie, a system in which the product K x V is substantially constant for each stage; and with this product constant, and assuming other factors such as the resistance of the circuits constant, the energy retransfer or feed back due to the grid plate capacity may be held invariant. In the preferred embodiment of the invention, the energy retransfer in the second tuning stage of the system is held constant, while the energ retransfer in the first tuning stage is ma e to deviate somewhat from a constant value and more specifically to decrease with increase of wave length so as tocompensate for the decrease of losses in the first in at circuit which takes place with increase 0 wave length, it being desired that the ener stant percentage of t e losses in such -input circuit. It is to compensate for such change or variation of losses that'the mutual for the first tuning stage is made to vary at a rate less than the power of the wavelength as heretofore set forth. The change in en'- ergy retrarls'fer in this first power of the wave length and maybe rey retransfer be a contuning stage, however, while it is made to vary for compen capacity with tubes having a low grid-plate capacity such as 3 micro-micro farads. I have discovered that for such tubes and with shunt capacities of 100 micro micro-farads, the feed back is of the right order throughout the wave length range.

With tubes of larger grid-plate capacity and approximately 8 micro-micro-farads, the above described features of my invention may be com bined ,with capacitive feed back control means for compensating for the remaining grid-plate capacity (5 out of 8 micro-microfarads), and for maintaining the retransferred energy in such tubes constant over the whole wave length range; and this, as heretofore set forth, comprehends a further prime object of my present invention.

The capacitive feed back control means which I combine with the inductive tuning and change of coupling coefficient features of my invention is that described and claimed in my copending application Ser. No. 607 ,oae heretofore referred to, the resulting system being shown in Fig. 6 of the drawings; In Fig. 6 of the drawings, I show a radio receiving circuit having two stages of radio frequency amplification similar to that heretofore described in connection with Fig. 1, the parts of which are indicated by similar reference characters, the system in Fig. 6 of the drawings further including an audio stage following the rectifying device a The amplifying circuits in Fig. 6 are substantially the same as that shown in Fig. 1, and are also indicated by similar reference characters, the variometer V being of the type shown in Fig. 3, the variotransformer V that shown in Fig. 4. and the variotransformer V that shown in Fig- 5 of the drawings.

For controlling, compensating or neutralizing the excess grid-plate capacitive feed back, I provide means inductively related to the variotransformers V and V for producin g a charge equal in magnitude but opposite in sign to the charge carried to the grid from the plate and for impressing such charge on the grid of each amplifying tube. This is accomplished by first creating a potential opposite to the potential on the plate and impressing the said potential on a condenser which is connected to the grid of the tube, the product of the potential and the capacity of the condenser being made equal to the excess charge transferred to the grid from the plate due to the inherent capacity therebetween.

Referring now to Fig. 6 of the drawings, I show such neutralizing means as comprising a coil B-P hereinafter called the reverse potential coil, inductively related to the end stator 8 of the variotransformer V, to which stator coil the primary L, is inductively coupled. the construction being such that a potential is created by the R--P coil which is made equal in phase and amplitude and opposite in sign to the potential on the plate 22;

and the reverse potential coil is connected by means of a conductor to a plate d of a condenser 56, another plate 6 of which is connected by means of the conductors 57 and 58 to the grid 21 of the tube a, the other end of the reverse potential coil being connected to the B battery by means of the conductor 28. The plate a of the condenser 56 preferably comprises a rotor so that the capacity of this condenser may'be varied to make the same equal to that capacity between the grid and plate of the tube which is desired to be co1npensated for. The reverse potential coil may if desired be coupled to the primary L but in the preferred construction both the reverse potential and primary coils are similarly and equally coupled tothe end stator coil 8 of the variotransformer, as clearly shown in Figs. 4: and 6 of the drawings.

For neutralizing the excess grid-plate capacity feed back of the tube a, the variotransformer V is similarly provided with a reverse potential coil R-P, which however is coupled to the end stator coil 8 by being arranged at the end of the variotransformer unit as clearly shown in Figs. 5 and 6 of the drawings, this reverse potential coil being connected at one end to the B battery by means ofthe conductor 38 and at the other end to the plate d of the condenser 56 by means of the conductor 59, the plate 0 of which condenser is connected to the grid 21 of the tube a by means of the conductors 60 and 23. Here too it will be noted that both the primary coil L and the reverse potential coil R-P are coupled equally to the end stator coil 8 By the provision of this means, it will be seen that the grid of each tube is supplied with an electric charge which is equal and opposite to the charge thereon resulting from the grid-plate capacity, and it will be further noted that the neutralizing charge varies in correspondence with the varying charge on the plate in the operation of the circuits so that the energy feed back is compensated for in all the frequency variations of the grid and plate circuits.

As above stated, the neutralizing condensers 56 and 56' are made adjustable for the purpose of varying the charge impressed on the grid. For the purpose of preventing the variation of capacity of these condensers from varying the tuning characteristics of the grid or input circuit, my invention further includes means for varying the capacity of the input circuit simultaneously and in correspondence with the varying of the capacity in the charge equalizing circuit. This result is accomplished in the preferred practice of my invention by making the condensers 56 and 56 in the form of three-element condensers each having an additional plate f which is connected to the filament end of the grid circuit by means of the conductors 61,

between the plates between the plates 0 62 for the condenser 56 and conductors 63, 64, 24, 25 and 62 for the condenser 56. The construction of the'plates e, f and d of each condenser is such that when the plate 0 is moved in one direction, the capacity between the plates 0 and d is increased and the capacity and f is correspondingly decreased, and as the plate 0 is moved in the opposite direction, the capacity between the plates (2 and f is increascd'while the capacity and d is correspondingly decreased. In view of the negligible impedance of the reverse potential coil as compared with the impedance of the grid coil, the change in capacity between the plates 6 and f is normally effective for modifying the capacity of the grid circuit, and by this construction the grid circuit capacity may be maintained constant during adjustment of the plate 6 and hence during the variation of the charge impressed upon the grid. The threeplate condenser of my invention preferably has a construction described and claimed in my copending application Ser. No. 680,465 filed Dec. 13, 1923.

In addition to the two radio frequency stages, I show in Fig.6 an audio frequency stage comprising an amplifying tube a having an input circuit 2' coupled to the output circuit 0 of the tube a by means of a transformer t, the audio frequency tube having an output circuit 0 provided with the usual telephone switch 65. In order to permit a shift of the telephones from the audio to the detecting stage of the system, the output circuit 0 is provided with the usual three-point switching device 66.

From the above it will further be seen that with my inductively tuned system, astability of feed back is obtained. The above considerations show that the total secondary re sistance B should increase with the wave length and that the percentage which remains after the tube feed back reaction should be approximately equally divided between real and primary reflected resistances- R and R, respectively. With the engineering materials commerically available it is not always possible to obtain low enough values of R and R,. Advantage should be taken, therefore, of the reduction of resistance R2)? due to the tube grid-plate feed back reactiom The great advantage of the inductively tuned system is that, as already remarked, with low capacity tubes the percentage reduction is approximately correct over the whole wave length range. WVith high capacity tubes using my feed back compensator system, a motion of the feed back reaction may be left active and the same fraction is effective for the whole wave length range. 7

Two conditions should be satisfied in order to secure stable operation, by which is meant avoiding oscillation or incipient oscillation conditions of the amplifier. The first is that tuned stages arranged R plus R be always greater than R The second is that R as above stated be comparable in magnitude with R The first condition means that the secondary circuit always has a net positive resistance; for, when the net resistance is zero or negative any oscillation set up in the secondary circuit persists indefinitely or increases its amplitude until the voltages exceed the linear li nits of the tube characteristics. The second condition is one which permits the first to be practically realized. If a circuit be constructed having low R and with a relatively high R, and the sum of these be almost completely negatived by R then the balance will depend primarily upon the constancy of R flected resistance, however, isagain dependent upon the filament plate resistance, which varies somewhat with the amplitude of the signal, with the B battery voltage, and quite sharply with the filament current. The usual and best way of controlling volume is by adj ustment of the radio frequency amplification through the adjustment of the filament current. Decreasing the filament current decreases the electron emission, increases the plate filament resistance and therefore decreases R A slight variation of the filament current of the preceding tube will carry the net resistance of the secondary circuit down to zero or to a negative value with resulting oscillations;

This re- As heretofore stated, it is a" further principal object of my invention to provide a radio receiving set having a number of inductively in cascade, in which intermagnetie coupling between the stages is effectively obviated, permitting independence of adjustment for each stage and permitting the units of all the stages to be mounted closely together without producing magnetic coupling troubles. I have discovered that when the double D variometers of adjacent stages are turned at right angles one with respect to the other with their axes parallel or with their axes coaxial, substantially all residual magnetic coupling between the stages is effectively eliminated. It will be understood that the variometers of the double D type have little intermagnetic coupling to begin with, especially so when the variometers are set with their axes parallel, the residual coupling diminishing very rapidly with increasing distance between the variomter axes. When the double D coils of aid-- jacent variometer or variotransformer units, however, are turned at right angles, this residual is practically nullified. The reason for this will be readily appreciated when it is seen that if the coils of all the units were arranged in the same way, the effect of one of the D coil sections of one unit upon a D section of an adjacent unit would be different than the effect of the other 1) section of the cent unit. Therefore by rotating one of the units 90 relatively to the other, the D section of one unit has the same coupling efi'ect on the two Ds of the adjacent unit, resulting in magnetic neutralizing effects, the neutralization being the result of the fact that the magnetic fieldsin the two D sections ofa given unit are in opposite directions. lVith this arrangement, therefore, all residual magnetic coupling between the units is practically el iminatcd or at least minimized to the lowest degree; and the units may be closely mounted without having magnetic coupling troubles.

\Vhere a variometer v and a plurality .of

"ariotransformers are arranged in series, as in Figs. 1 and 6, I have found that the optimum condition of elimination of residual coupling is reached when the D coils (that is to say the stator D coils and the rotor D coils for the same setting) of the intermediate unit are arranged at right angles to the D coils of the outside units. This phase of my invention is clearly depicted in Fig. 1 of the drawings, in which it will be seen that the coils of the variotransformer V are arranged at an angle of 90 to the coils of the variometer V and the variotransformer V 1 Although the position of the rotor coils varies when the stage is tuned, it will be understood that the rotor coils of the different stages bear to one another the desired relation, since the circuits are designed, as hereinbefore fully set forth, to tune in the same way and with substantially the same rotor settings.

The manner of making and using the tuned radio frequency system of my invention will in the-main be fully apparent'from the above detailed description thereof taken in conjunction with the operations as heretofore outlined. It will be further apparent that while I have disclosed in detail the construction and arrangement of the system and the parts thereof With the particular magnitudes or sizes of the capacities and inductances involved, that my invention is not to be limited thereto, and that changes may be made within wide limits as hereinbefore set forth without varying from the principles of my invention as defined in the following claims.

I claim:

1. The combination of an electron dis charge device having a cathode, an anode and a grid, a circuit connected to the anode of the device and a second circuit coupled to the said anode circuit, the saidcoupled circuits including mechanism predetermined in its operation for simultaneously varying in the samedirection the coupling coefficient of said circuits and the wave length of the said second circuit.

2. The combination of an electron dis charge devic-ehaving a cathode, an anode and a grid, a circuit connected to the anode of the device, a second circuit, means coupling said second circuit to the said anode circuit, means for tuning'said coupled circuits and mechanism connecting both of said means for simultaneously varying in the same direction the coupling coefficient between said circuits and the wave length of the said second circuit. 1 ,7

3. The combination of an electron discharge device having a cathode, an anode and a grid,'a circuit connected to the anode of the device and a second circuit inductively coupled to the said anode ci1'cuit,-tl1e said coupled circuits including mechanism for inductively tuning the said second circuit and for simultaneously varying the said induc tive coupling in a predetermined manner.

4.."l7he combinationof an electron discharge device having a cathode, an anode and a grid, a circuit connected to the anode of the device and a second circuit coupled to the said anode circuit, the said coupledcircuits including mechanism predetermiend in itsoperation for simultaneously and progressively varying'in the same direction the said coupling and the wave length of the said second circuit, whereby the coupling is relatively loose on the shorter Wave lengths and relatively tight on the longer wavelengths.

5. The combination of an electron discharge device having a cathode, an anode and a grid, a circuit connected to the anode of the device and a second circuit coupled to the said anode circuit, the said coupled circults lncluding a variotransform'er having a primary in the anode circuit and a variable secondary in the second circuit and means for simultaneously varying the coupling coefficient between the primary and secondary circuits and the tuning of the second circuit.

6. In combination, a plurality of electron dischargeube circuits, means for inductively linking the circuits in cascade, means for tuning the coupled circuits and mechanism connecting both of said means for simultaneously arying in the same direction the couplingcocfiicient between adjacent circuits and the wave length of one of the circuits, whereby the coupling is relatively loose on shore- Wave lengths and relatively tight on long wave lengths.

7. In combmation, an electron discharge .device having an output circuit and an input circuit, and means for linking the circuits in cascade including mechanism for simultaneously and progressively varying in a predetermined'manner the coupling coefiicient between adjacent circuits and the wave length of one of the circuits in the same direction.

8. The combination of a plurality of electron discharge devices each having a cathode. an anode an'd'a gride. and means for linking the devices in cascade including a circuit connected to the anode of one device and a circuit inductively coupled to the anode circuit and connected to the grid of the second device, the said coupled circuits including mechanism for inductively tuning the said grid circuit and for simultaneously varying the said inductive-coupling in a predetermined manner.

9. The combination of a plurality of electron discharge devices each having a cathode, an anode and a grid, and means for linking the devices in cascade includinga circuit connected to the anode of one device and a circuit coupled to the anode circuit and connected to the grid of the second device, the said coupled circuits including mechanism predetermined in its operation for simultaneously varying in the same direction the coupling coefficient between said circuits and the wave length of the said grid circuit.

10. The combination of a plurality of electron discharge device each having a cathode, an anode anda grid, and means for linking the devices in cascade including a circuit con-- nected to the anode of one device and a circuit coupled to the anode circuit and con nected to thegrid of the second device, the said coupled circuits including a variotransformer having a primary in said anode cir cuit and a variable secondary in said grid circuit and means for simultaneously varying the coupling coeliicient between the primary and secondary circuits and the tuning of the secondary.

11. In combination, a plurality of circuits and means for linking the circuits in cascade including mechanism predetern'iincd in its operation for varying the wave length of one of the circuits and for simultaneously varying the coupling coeflicient between the circuits substantially proportionately to and in the same direction as the wave length variation. i

12. The combination of an electron discharge device having a cathode, an anode and a. grid, a circuit connected to the anode of the device and a second circuit coupled to said anode circuit, the said coupled circuits including means for varying the wave length oi? said second circuit, means for varying the coupling of the circuits and mechanism connecting both of said means for simultaneously varlving the coupling coeiiicient between the circuits substantially proportionately to and in the same direction as the wave length variation.

13. The combination of an electron discharge device having a cathode, an anode and a grid, a circuit connected to the anode of the device and a second circuit inductively coupled to said anode'circuit, the said coupled circuits including mechanism for inductively varying the wave length of said second circuit and for simultaneously varying the coupling coeliicient between the circuits substanlinked thereby in the same direction with and proportionately to the variation of the wave length in one of the circuits linked thereby.

15. In combination, a series of cascaded circuits including a plurality of structures each linking adjacent circuits of the series, one of the said structures including mechanism for simultaneously varying the coupling coeflicient of the circuits linked thereby in the same direction with andjless than proportionately to the variation of the wave length in one of said linked circuits and the other of said structures including mechanism for simultaneously varying the coupling coeiiicient of the circuits linked thereby in the same direction with and proportionately to the variation of the wave length in one of the circuits linked thereby.

16. The combination of an electron discharge device having cathode, an anode and a grid, a circuit connected to the anode of the device and a second circuit coupled to said anode circuit, the said coupled circuits including mechanism for varying the Wave length of said second circuit and for simultaneously varying the coupling coefficient between the circuits less than proportionately to and in the same direction as the wave length variation.

17. The combination of an electron dis charge device having a cathode, an anode and a grid, an output circuit connected to the anode of the device and an input circuit coupled to the said output circuit, the said coupled circuits including mechanism for simultaneously varying in a predetermined manner the coupling coefficient between the cir cuits and the tuning of the input circuit, the said output circuit having an impedance which is substantially one-half the plate-film ment impedance. 7 a

18. The combination. of a phuality of electron discharge devices each having a cathode, an anode and a grid, and means forlinking the devices in cascade including an output circuit connected to the anode of one device and an input circuitcoupled to the output circuit and connected to the grid of the second device, the said coupled circuits including mechanism for simultaneously varying in a predetermmed manner the coupling coclhclent between the circuits and the tuning 0t said input circuit, the impedance of the said output circuit being substantially one-half the late filament impedance.

19. The combination of an electron discharge device having a cathode, an anode and a grid, an output and primary circuit connected to the anode of the device and an input and secondary circuit coupled to the said primary circuit, the said coupled circuits including mechanism for simultaneously varying in a predetermined manner the coupling coetlicient between the circuits and the tuning of the secondary circuit, the said circuits having resistances of a magnitude such that the resistance reflected from the primary into the secondary is of the same order of magnitude as the ohmic resistance of the secondary.

20. The combination of an electron discharge device having a cathode, an anode and a grid, an input circuit connected to the grid, an output circuit connected to the anode, capacity means in the said input circuit having a. total shunt capacity value which is of a magnitude of from ten to twenty times the grid-plate capacity of the device, and means for tuning the said input circuit while keeping the said total shunt capacity value substantially constant.

21. The combination of an electron dis charge device havingacathode, an anode and a grid, an input circuit connected to the grid, an output circuit connected to'theanode, a variable inductance in the said input circuit for tuning the same, and capacity means-in said input circuit having a total shunt capac ity value which remains substantially constant during tuning of the circuit and of a magnitude of from ten to twenty times the grid-plate capacity of the device.

22. The combination of an electron discharge device having a cathode, and anode and a grid, an input circuit connected to the grid including a variable inductance for tuning the input circuit, an output circuit connected to the anode, a condenser in shunt with the variable inductance substantially equal in magnitude to the capacity of the remaining part of the input circuit.

23. The combination of an electron discharge device having a cathode, an anode and a grid, an input circuit connected to the grid including a variable inductance for tuning the input circuit, an output circuit connected to the anode, a condenser'in shunt with the variable inductance having a capacity from ten to twenty times the grid-plate capacity of the device. I

24. In combination, a plurality of electron discharge devices each having a cathode, an anode and a grid, and means for linking the said devices comprising coupled anode and grid circuits including a variotransformcr the anode circuit'and a having a primary 1 variable secondary 1n the grid circuit for tuning the latter, and a condenser in shunt to the variable secondary of a magnitude substantially equal to the capacity of the remaining part of the grid circuit.

25. The combination of an "electron dis charge device having a cathode, an anode and a grid, an input circuit connected to the grid, an outputcircuit connected to the anode, a circuit coupled to the said output circuit and including mechanism for inductively tuning the coupled circuit, and feed-back control means for compensating for the capacity coupling between the grid and plate of said device.

'26. The combintion of an electron discharge device having a cathode, an anode and a grid, an input circuit connected to the rid, an output circuit connected'tothe anode, a circuit inductively coupled to the said output circuit and including mechanism for induc tively tuning the coupled circuit, and feedback control means inductively associated with both the output circuitand the coupled circuit for compensating for the capacity coupling between the grid and platepf said device.

27. The combination of an electron discharge device having a cathode, an anode and a grid, an input circuit connected to the grid, an output circuit connected to the anode, a

circuit coupled to the said output circuit and I including mechanism for inductively tuning the coupled circuit, and feed-back control means for compensating for the capacity coupling between the grid and plate of said device. the said compensating means comprising a condenser, connected to the grid and a coil"nduct'vely coupled to said coupled circuit and connected to said condenser.

28. The combination of an electron discharge device having a cathode, an anode and av grid, an input circuit connected to the rid. iinode. a circuit coupledto the said output circuit and including mechanism for inductively tuning the coupled circuit and for simultaneously varying the coupling coefiicient, and feed-back control means for compensating for the capacity coupling between the grid and plate of said device.

29 The combination of an electron discharge device having acathode, an anode and a grid, a circuit, and means for linking the circuit to the anode of the electron discharge device, the said means comprising a variotransformer having a primary connected to the anode of said device and a variable secondary in said circuit, and feed-back control means inductively related to said variotransformer for compensating for the grid-plate capacity of said device.

30. The combination of an electron discharge device having a cathode, an anode and a grid, a circuit, and means for linking the circuit to the anode of the electron discharge an output circuit connected to the device, the said means comprising a vario-.

transformer havin a primaryconnected to the anode of said do ondary in said circuit, and means for compensating for the'gridrplate capacity of said device comprising a 0011 inductively related to said variotransformer. and a condenserconnecting the coil to theigrid. 31. The combination of an electron discharge device having acathode, an anode and a grid, a circuit, and means for linking the charge device, the said means comprising a v variotransformer having a primary connected to the anode of sand device and a variable secondary in said circuit made up of stator and rotor double D coils, and means inductively related to a stator coil of said variable secondary for compensating for the gridplate ca acity ofs aid device.

33. T e combination of an electron dis charge device having a cathode, an anode and a grid, a circuit, and means for linking the circuit to the anode of the electron discharge device, the said means comprising a variotransformer having a primary connected to the anode of said evice and a varlable secondary in said circuit made up of stator and 1 rotor double D coils, and means inductively related to a coilof said variable secondary for com ensating for the grid-plate capacity of said evice. p

34.- The combination of an electron discharge device having a cathode, an anode and a grid, a circuit, and means for linking the circuit to the anode of the electron discharge device, the said means comprising a variotransformer having a primary connected to the anode of said device and a variable secondary in said circuit made up of stator and rotor double D coils, and means including a coil inductively related to a stator coil of said variable secondary for compensating for the grid-plate capacity of said device, the said primary being also inductively related to said stator coil.

85. The combination of an electron discharge device having a cathode, an anode and a grid, an antenna circuit connected to the (grid, an output circuit connected to the the said antenna circuit having a variable inductance for tuning purposes and vice and -a variable secin said circuit, and means having a acity of said device the said ductively 7 grid, an input,circu1t connected to the having-a total shunt capacity which remains substantially constant during tuning of thecircuit and of a magnitude of from ten to twenty times the grid-plate capacity of the device.-

36. The combination of an electron dis-qv charge device having a cathode, an anode and a grid, an antenna circuit connected to the grid, an output circuit connected to the anode, the said antenna circuit/having a variable inductance for tuning purposes and havin a total shunt capacity which remains su stantially constant during tuning of the circuit and of a magnitude of from fift to one hundred and fifty micro-micro-fara s.

- '37. The combination of an electron discharge device having a cathode, an anode and a grid, an output circuit connected to the an- 5 ode, said output circuit having a predeten mined impedance, and a second circuit coupled to the anode circuit, the said coupled circuits including mechanism for tuning the second circuit while maintaining the output impedance of the output circuit substantially constant. 1

38. The combination of an electron discharge device having a cathode, an anode and a grid, an output circuit, connected to the anode, said output circuit having a predetermined impedance, and a second circuit inductively coupled to the anode circuit, the said coupled circuits including mechanism for in ductively tuning the second circuit while maintaining the output impedance of the output circuit substantially constant.

39. The combination of an electron discharge device having a cathode, an anode and a (grid, an outputcircuit connected to the ano e and a'second circuit inductively coupled to the anode circuit the said coupled circuits including mechanism for tuning the second circuitjhaving ohmic resistance and mutual inductance quantities which maintains the out ut impedance of the output circuit substantially constant.

40. The combination of an electron discharge device having a cathode a plate and a grid, an output circuit connected to the plate, another circuit coupled to the plate circuit, means for compensating for the capacitive feed back reaction due to the grid-plate capacity, the said coupled circuits including mechanism for tuning the said other circuit without changing the capacity thereof whereby the capacitive coupling'coeflicient between the input and output circuits remains constant during such tuning of the said other circuit.

41. The combination of an electron discharge device having a cathode, a plate and a grid, an input circuit connected to the grid, an output clrcuitcontaining impedance connected to the plate, another circuit coupled to the plate circuit and means for tuning the uct of the output impedance, the oscillating plate current and the capacitive coupling c0- eflicient between the'grid and late circuits substantially constant during t e tuning of said other circuit.

42. The combination of an electron discharge tube having a cathode, a plate and a grid, a grid circuit connected to the grid of to the plate of the tu e, a third circuit embodying means for variably tuning the same, means coupling the said untuned plate circuit to said tunable circuit, and meansfor varying the coupling of saidcoupling means for compensating the effects resulting from the varying of said tuning means. 43. The combination of an electron discharge tube having a cathode, a plate and a grid, a grid circuit connected to the grid-of the tube, an untuned plate circuit connected to the plate of the tube, a third circuit embodying means for variably tuning the same, means coupling the said plate circuit to said tunable circuit, and means for varying the said couplingmcans as the said tuning means is varied. v

44. The combination of an electron discharge tube having a cathode, a plate and a grid, :1 grid circuit connected to the grid of the tube, a plate circuit connected to the plate of the tube, a third and tunable circuit embodying means for variably tuning the same,

I means coupling the said plate circuit to said tunable circuit, and means for varying the coupling of said coupling means, the said plate circuit comprising a primary'havin a natural frequency which is reater than t e highest frequency of the Frequency range through which said tunable circuit is tunable, the said primary being coupled to said tunable circuit so that a change of coupling be- Y tween the primary and the tunable circuitis unaccompanied by a change of capacity across said tunable circuit.

45. The combination of an electron discharge tube having a cathode, a plate and a grid, a" grid circuit connected to the grid of the tube, a plate circuit connected to the plate of the tube, a third and tunable circuit embodying means for variabl tuning the same, means coupling the said p ate circuit to said tunable circuit, and means for varying the coupling of said coupling means, the sa1d plate circuit comprising an untuned plate coil primary having a natural frequency beyond the frequency range through which said tunable circuit is tunable, the said primary being coupled to the low potential end of said tunable circuit whereby a change of coupling between the primary and the tunable circuit is unaccon'ipanied by a change of capacity across said tunable circuit.

late circuit connected 46. A radio circuit system comprising a plurality of stages arranged in cascade or series, a transformer embodying a primary and a secondary coupling one of said stages to an adjacent stage, means for tuning the circuit of said adjacent or secondary stage over a range of frequencies, means for varying the coupling between the primary and the secondary of the transformer, the con-.

stants of the coupled stages including a natural frequency for the transformer primary which is greater than the highest frequency of the frequency ran e through which the secondary stage is tuna lo, the said primary being coupled to said secondary so that a change of coupling between the primary and second ary of the transformer is unaccompanied by a change of capacity across the tuned seconda I ary stage, j 47. A radio circuit' system comprising a plurality of stages arranged incascade or series, a transformer embodying a primary and a secondary having a high step-up ratio coupling one of said stages to an adjacent stage, the low potential end of the secondary stage being connected to ground, means for tuning the circuit of said adjacent or secondary stage over a range of frequencies, means for varying the coupling between the primary and the secondary of the transformer, the constants of the coupled stages including n natural frequency for the transformer'primary which is beyond or outside of the frequency range through which the secondary stage is tunable, the said primary being coupled to the ground potential end of said secondary.

48. A radio circuit system comprising a plurality of stages arranged in cascade or series including on electron discharge tube stage, a transformer embodying a primary and a secondary having a high step-up ratio coupling the tube stage to an adjacent stage, means for tuning the circuit of said adjacent or secondary stage over a range of frequencies, means for varying the coupling between the-primary and the secondary of the transformer, the constantsof said coupled stages including a natural frequency for the transformer primary which is beyond or outside of the frequency range through which the secondary stage is tunable, the said primary cuit' of said adjacent or secondary stage over a range of frequencies, means connecting the low potential end of the secondary stage to ground, means for varying the coupling between the primary and the secondary of the transformer, the constants of said coupled stages including a natural frequency for the transformer primarywvhich is greater than the highest frequency of the frequency range through which the secondary stage is tunable, the said primary being coupled to the ground potential end of said secondary.

50. A radio circuit system comprising a plurality of stages arranged in cascade or series including a vacuum tube stage, a transformer embodying a primary and a secondary coupling the tube stage to an adjacent stage, means for tuning the circuit of said adjacent or secondary stage over a range of frequencies, means for varying the coupling between the primary and the secondary of the transformer, the constants of the coupled stages including an input conductance for the transformer at resonance substantially higher than the plate conductance of the vacuum tube, the said primary being coupled to said secondary so that a change of coupling between the primary and secondary of the trans former is unaccompanied by a change of capacity across the tuned-secondary stage.

51. A radio circuit system conu'irising a plurality of stages arranged in cascade or series including a vacuum tube stage, a high step-up ratio transformer embodying a primary and a secondary coupling the tube stage to an adjacent stage, means for tuning the circuit of saidadjacent or sccondary stage overa range of frequencies, means for varying the coupling between the primary and thesecondary of the transformer, the constants of the coupled stages including an input conductance for the transformer at resonance substantially higher than the plate conductance of the vacuum tube, means connecting the low potential end of the secondary stage to ground, the said primary being coupled to the ground potential end of said secondary.

52. The method of operating a tuned radio .t'requcncy amplifier including a vacuum tube and an output transformer associated therewith which consists in arranging the input conductance of said output transformer at rcsonance's'o that it is substantially higher in value than the plate conductance of the vacuum tube, in tuning the secondary of said transformer and in varying the coupling between the primary and secondary of said transt'orn'ier without appreciably changing the effective capacity across the tuned secondary of the transformer. i

53. The method of operating a tuned radio frequency amplifier including a vacuum tube whose plate circuit is connected to the input terminals of an electric coupling system, and a second vacuum tube whose grid'is connected to the output terminals 01: said coupling system \vh ich consists in arranging said coupling system to step-up the voltage at resonance and to have an input conductance at resonance substantially higher in value than the plate conductance of the first mentioned vacuum tube, in tuning the secondary of said coupling system and in varying the coupling" between the primary and secondary of said coupling system without appreciably changing the eli'ective capacity across the tuned secondary of the coupling system.

Signed at New York city, in the county .of New York and State of New York, this 24th day of May, A. D. 1924:.

LESTER L. JoNEs. 

